Cornea

The clear, dome-shaped outer layer of the front of the eye is the cornea of the eye. The cornea covers the anterior chamber, the iris, and the pupil beneath it. Unlike most other tissues in the human body, corneal tissues don’t have any blood vessels (except at their margins). It gets its nourishment from the aqueous humor, posteriorly and by tears, anteriorly. Irregularity in the curvature of the cornea leads to astigmatism. Every time we blink our eyes, the tears wipe out the cornea throughout its surface, thereby keeping it moist and resists infection. It is very sensitive to touch and pain.

Composition of the Cornea

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The cornea is composed of five layers -

Epithelium, which is made of epithelial tissues, is regenerative in nature. Any irregularity in epithelium affects the total refractive power of the eye, thus unbalancing visual capability.

Bowman’s layer, which is composed of tightly-woven collagen fibrils, is a 14-micrometer thin layer that protects the corneal stroma.

Stroma, which is a thick collagen layer (comprises almost 90 percent of the cornea) plays a major role in the transparency of the cornea due to its arrangement of fibers.

Descemet’s membrane, the acellular membrane acts as the base layer for the corneal endothelium.  

The endothelium, the innermost layer regulates the fluid transport thereby preventing the cornea from being over swollen. They don’t regenerate, rather the existing cells stretch to compensate for the void developed.

Function of the Cornea:

The cornea of the eye contributes mostly to the focusing power of the eye where it refracts the incoming light on the lens and focuses light on the retina; the epithelium provides a surface for optimum moisture and helps in clear and stable vision; the bowman’s layer prevents abrasions and scratches, and the endothelium maintains the fluidity within the cornea.

Corneal Disorders:

The disorders related to the cornea are –

1.    Keratoconus

A. Condition – in such cases the collagen fibers of the cornea of the eye weakens and thins out due to which it can’t retain its shape and so, it bulges outwards giving a conical shape.

B. Causes – the exact reasons for keratoconus are unknown but environmental factors and genetics play a huge role in this.

C. Symptoms – a person suffering from keratoconus is likely to face symptoms like

i. blurred vision

ii. sensitivity to light

iii. poor dim light vision

iv. discoloration around the eye

D. Treatment – initially the victim is prescribed glasses when the symptoms are mild. For extensive cases, the prescribed methods are as follows

i. contact lenses which might be used like soft contact lenses, gas permeable contact lenses, hybrid contact lenses, and prosthetic lenses.

ii. Corneal cross-linking

iii. Corneal transplant

2. Corneal Arcus

A. Condition – in such cases the cornea is deposited with cholesterol and phospholipid at its periphery which forms a faint blue or grey ring.

B. Causes – due to decreased lipid metabolism, lipid deposits at cornea’s edge. Also, individuals with high cholesterol build up cholesterol crystals both in the central and peripheral cornea.

C. Symptoms – a person suffering from corneal arcus is likely to face symptoms involving

i. The arc sharpen at the outer border and starts fainting inwards

ii. The arc might grow to form a full ring, thereby covering the entire iris

D. Treatment – corneal arcus is generally not a matter of concern for victims aging above the 50s but if below that, chances are the victim has a high cholesterol level and needs an immediate check.

3. Corneal Dystrophy

A. Condition – it is a rare hereditary condition where abnormal material or foreign substances accumulate in the layers of the cornea progressively. There are primarily three types of dystrophies

i. Superficial or anterior corneal dystrophy

ii. Stromal corneal dystrophy

iii. Posterior corneal dystrophy

B. Causes – due to genetic mutations, transcription of aberrant protein occurs in the cornea.  

C. Symptoms – the symptoms are as follows

i. Corneal erosion

ii. Blurry vision or loss of vision

iii. Sensitivity of light or glare

iv. Pain in the eye

D. Treatment – initially the doctor prescribes eye drops or ointments. In severe cases, corneal transplantation is required.

Solved Examples:

1. Is a Corneal Transplant Painful?

Ans: Generally, before the transplant surgery, eye drops and anesthesia are dosed to relax and numb the eye. During the surgery, there is a negligible sensation of pain but slight pain might be felt after the effect of anesthesia is over. Doctors prescribe eye drops for pain relief.

2. What is Corneal Blindness?

Ans: When the cornea is covered due to any reason, light is unable to pass through it to the light-sensitive retina and the victim is unable to see. This condition is called Corneal blindness.

Conclusion:

The cornea of the eye can repair itself from minor abrasions but in severe cases, it might lead to the damaging of the corneal tissues which affects its transparency and the visual capability of the person.

If neglected, corneal disorders can lead to eye pain and loss of vision in the victim. Hence, consulting a doctor at the earliest is advisable.